Understanding circulatory and non-circulatory shock

I find it best to think of the circulation as a fuel delivery system and shock as what happens when the energy supply dries up. Your car certainly has a fuel delivery system: gasolene is pumped from the tank to the cylinders where it undergoes combustion in the presence of oxygen. If the gas tank is empty, or the pump is broken, or there is no oxygen, or the spark plugs aren’t firing, the engine will not run.

Water is a fuel for plants that use it in combination with carbon dioxide for photosynthesis. Thus, in arid environments, a water irrigation system is a fuel delivery system. The categories of shock that humans can experience may be best understood using this analogy:

Hypovolemic shock: Low water tank level. If there is insufficient water to deliver to all the plants, plant growth and/or life is impaired.

Cardiogenic shock: Pump failure. If the pump fails so that water is not delivered to the plants, it produces the same result as not having enough water.

Neurogenic “shock.”: Bigger pipes. In neurogenic shock, blood vessels dilate because the sympathetic nervous system is impaired. This larger pipe diameter does not actually reduce fuel deliver. Yes, the driving pressure in the system is lower, but the resistance to flow is less due to the larger diameter. Hence, the flow of fluid is usually normal.

Septic shock: Poisoning. The irrigation system is working just fine. In fact, it’s working better than normal. However, the plants are still dying. The only conclusion the farmer can draw is that some pest or poison is killing his plants. He would not conclude that there’s a problem with the irrigation system.

Unfortunately, in modern medicine, there is a great deal of confusion over the latter two versions of shock. Physicians often read the low blood pressure in neurogenic shock and assume that it must be fixed. While providing more intravenous volume may help ensure adequate blood flow to tissue, the use of vasoconstrictors does not. Similarly, in septic shock, it is difficult to understand how overcoming a compensatory vasodilatory response with vasoconstriction can change the fundamental problem of inadequate oxygen consumption by the cellular machinery. There needs to be a paradigm shift in medicine’s understanding and management of the various physiologic shock states.